4R/22L and 4L/22R are the primary runways for GA operations, not the Reef Runway. In any case, GA run-ups at HNL are completed on the tarmac space on the South Ramp which is where all the GA facilities are located. After your run-up, you would contact HNL Ground Control for clearance/taxi instructions.

Some runways don't have run-up pads. I can think of numerous airports that don't. In that case, you just do your run up at the hold short line/in sequence or find some empty ramp space where you won't be prop blasting anything.

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